1. Field of the Invention
The present invention pertains to the art of dishwashers and, more particularly, to a drain pump assembly employed in a dishwasher, preferably a drawer-type dishwasher.
2. Discussion of the Prior Art
In a typical dishwasher, washing fluid is pumped from a sump into upper and lower wash arms such that kitchenware, retained on vertically spaced racks within a tub of the dishwasher, will be sprayed with the washing fluid for cleaning purposes. The washing fluid is heated, filtered and recirculated through operation of a wash pump. Prior to recirculating the washing fluid, some or all of the fluid is directed through one or more filters to remove soil from the fluid, with the soil being collected in one or more chambers. Periodically, the system will be purged in order to drain the collection chamber(s) of the soil, as well as the washing fluid from the overall dishwasher.
In many dishwashers, the wash pump is provided with a chopper blade that is rotated about an apertured chopper plate to macerate soil particles entrained in the washing fluid. The wash pump can either be designed to macerate the food particles prior to recirculation or, upon draining the washing fluid from the washing chamber, macerate the soil particles during a drain operation. Regardless of the particular configuration, it has been found that incorporating the chopper blade into the wash pump increases noise output by the dishwasher. As the demand for quiet appliances is on the rise, this configuration requires re-design.
One proposed solution is to add a second or drain pump to the dishwasher. The drain pump can be fitted with the chopper blade so that soil particles are macerated only during operation of the drain pump. Due to the fact that the drain pump is operated less frequently than the wash pump, the overall noise produced by the dishwasher can be reduced. However, in addition to noise considerations, size, and particularly vertical height, is also a consideration when designing a dishwasher. Thus, adding a second pump to the dishwasher presents a different set of design considerations. Fortunately, in contrast to recirculating fluid within the dishwasher where high pressure is required, drain pumps do not have a corresponding high pressure requirement. Instead, a drain pump need only overcome a pressure head maintained in a siphon loop of a drain hose. Therefore, a relatively small pump can be used to drain washing fluid and soil from the dishwasher.
While smaller pumps can generate sufficient pressure to perform a drain operation, the smaller pumps typically employ a synchronous motor and produce less torque. That is, when operating a chopper mechanism, the smaller pump cannot rotate a chopper blade with as much torque as a larger pump. If the chopper blade encounters a hard or large soil particle, the pump could stall or jam. When a stall condition occurs, the synchronous motor must restart, causing the chopper blade to repeatedly impact the large/hard soil particle. That is, when the synchronous motor restarts, the chopper blade oscillates back and forth “hammering” the soil particle until the particle becomes small enough to pass through the apertured plate. While effective, it may take some time to fully break up the soil particle as the smaller pump cannot impart a high degree of inertia to rotate the chopper blade. Also, while the synchronous motor is stalled, draining is postponed until the particle can pass through the apertured plate. Obviously, this interaction can create a substantial amount of noise, as well as lengthen an overall wash operation.
Another consideration when constructing a drain pump is the overall construction and assembly of the pump. Minimizing potential leakage points is critical. Therefore, the drain pump should be constructed so as to reduce the number of openings or joints that could act as potential leakage points. Ideally, the drain pump would be formed from a one piece housing into which all the components are installed. However, when positioning components in a one piece housing, it can be difficult to locate the chopper blade relative to the chopper plate and to connect the pump with a pump motor. Too large a gap between the chopper blade and the chopper plate will allow soil particles to become trapped or stuck in openings that are arrayed about the apertured plate. Too small a gap and the chopper blade can become jammed or could come in contact with and abrade the chopper plate, resulting in damage to either one or both components.
Based on the above, there still exists a need for an enhanced drain pump for a dishwasher, preferably a low profile drain pump that operates a chopper blade to macerate soil particles in a washing fluid. In addition, there exists a need for a drain pump that includes an alignment device that assures proper positioning of the chopper blade relative to an apertured chopper plate.